I'm a fan of diversification. That's why you'll find more than 70 individual stocks in my portfolio.

I'm also a big believer in letting your winners run. Following this investing philosophy has served me well over the years, but it has also caused my portfolio to be more concentrated than you might assume.

My top five holdings are MercadoLibre (NASDAQ:MELI), Booking Holdings (NASDAQ:BKNG), Mastercard (NYSE:MA), Netflix (NASDAQ:NFLX), and Amazon.com (NASDAQ:AMZN). Collectively, these businesses comprise more than a third of my portfolio.

Here's why I have no plans on parting ways with these stellar businesses anytime soon.

Arrows pointing up and growing taller

Image source: Getty Images.

MercadoLibre -- 5% of my portfolio

MercadoLibre is an e-commerce platform that primarily operates in Latin America. The company has been following in the footsteps of eBay for years and has grown at a breakneck pace. Investors who bought into this stock during its 2007 IPO are already sitting on a 10-bagger.

MercadoLibre makes its money in a handful of ways, but its most important services are its marketplace business, payment business, and shipping service.

The marketplace business connects buyers with sellers. MercadoLibre pulls in revenue from each successful transaction that takes place on its platform.

MercadoLibre also has its own PayPal-like payment system called MercadoPago that facilitates transactions. The company rakes in a small fee from processing each payment.

Finally, the company is building out its own fulfillment network to handle package delivery. This delivery and logistics platform helps sellers get items to where they need to be reliably and quickly. 

All of these business units have grown strongly over the last few years and still offer huge potential for growth. The primary reason for this is that only 55% of people in Latin America are currently online. Over time, this number should continue to catch up to developed countries like the U.S., where the internet penetration rate is closer to 90%. Layering in the general shift toward e-commerce should ensure that this business pumps out double-digit growth for a very long time.

Booking Holdings -- 6% of my portfolio

Consumers used to rely on travel agents to help them book vacations. Then companies like Booking Holdings burst onto the scene and made it easy for anyone to make their own reservations online and save a bundle in the process. The rest is history.

Booking Holdings has been the top dog in the move to online travel for years thanks to its portfolio of top-tier brands. This company owns a number of leading travel sites like Priceline.com, Kayak.com, RentalCars.com, Agoda.com, Booking.com, and more.

Booking owes a lot of its success to its early entry on the European hotel market. The company spent years building out a vast network and became the go-to choice for travelers and operators alike. That helped to fuel enormous growth, and Booking turned out to be a grand-slam investment.

The great news for investors is that the global shift toward online travel still has plenty of room left for continued growth. That's why Booking Holdings is still producing double-digit revenue and profit growth to this day, even though it is already a massive business.

This is a trend I think can persist for years to come, so I plan on remaining a happy shareholder indefinitely.

Mastercard -- 6% of my portfolio

Payment processors like Mastercard have been prime beneficiaries in the war on cash. Consumers increasingly prefer to pay with plastic since doing so provides speed and convenience that cash or check simply cannot match. 

Mastercard plays a pivotal role in ensuring that funds can easily flow between consumers, banks, and merchants. Mastercard charges a tiny fee for each transaction that flows through its network. Since billions of transactions occur on its network each year, those fees add up fast. The company pulls in billions in revenue and profit annually.

The beauty of this business model is that the majority of Mastercard's costs are fixed. This means incremental volume helps to drive enormous operating leverage and leads to out-sized growth on the bottom line.

Best of all, there is still a huge amount of room left for continued growth. Roughly 80% of worldwide transactions still occur using cash or check. Mastercard's revenue and profit should continue to steadily head higher as the shift to plastic marches on.

Netflix -- 9% of my portfolio

I first become a shareholder of Netflix about a decade ago. The company was primarily a DVD-by-mail business that was just starting to dabble in streaming. I had no idea it was about to become the leader in the shift away from the linear TV.

You know what happened next. The company used its DVD-by-mail profits to fund content growth and a massive expansion into international markets. That bold move has lead to explosive growth in subscribers and has set off a flywheel that has allowed its top line to surge. Long-term shareholders have been hugely rewarded for watching the story unfold. 

More recently, the company has been flexing its pricing muscles in an effort to turbo-charge revenue growth. Consumers have swallowed the increases without much of a fuss.  

The bull case for owning Netflix moving forward is that content costs will eventually flatten out and drive enormous profit growth as its subscriber count continues to surge. That's a story I find highly appealing, so I'm happy to continue holding my shares of this perennial winner.

Amazon.com -- 9% of my portfolio

Amazon.com easily ranks as one of my biggest winners of all time. I first started buying shares of the e-commerce titan in 2010. I thought I was late to the party and that the company was already too big to own. Shares are up more than 10-fold since.

It is easy to make the same argument today. Amazon's market cap briefly crossed $1 trillion last fall. How can an outsized investment in this company possible make sense?

I'd answer that question with the following:

  • E-commerce still only represents about 10% of total retail spending in the U.S. The number is even smaller in international markets, leaving ample room for continued growth in Amazon's core market. 
  • Amazon Web Services is a high-margin business that is growing like gangbusters and pumping out profits.
  • Advertising is a high-margin business that is showing tremendous growth and provides a long-tail opportunity.
  • Amazon Prime is hugely popular, growing by double-digits, and keeps shoppers coming back for more.

These four growth channels alone offer plenty of reasons to remain bullish, but the picture looks even better when you throw in other growth drivers like Whole Foods, Amazon Go, Twitch, Alexa devices, and potential moonshot projects like its steady move into healthcare.

In other words, Amazon still looks poised for massive growth in the decades ahead. That's why I plan on remaining a shareholder in this amazing business for years to come.